1. Field of the Invention
The present invention relates to disk drives for computer systems. More particularly, the present invention relates to a production line spindle control circuit employing a sinusoidal driver with back EMF control.
2. Description of the Prior Art
The spindle motor in a disk drive is typically driven by trapezoidal currents which can induce vibrations in the spindle motor. FIG. 1 shows example trapezoidal currents for driving a three phase spindle motor (comprising windings A,B,C) together with a spindle clock signal defining the commutation intervals and a back EMF zero crossing signal detected during a xe2x80x9cwindowxe2x80x9d while a selected one of the windings is not being driven. When manufacturing disk drives, a production line spindle control circuit is typically employed to control the spindle motor while performing various operations, such as diagnostics or servo writing. The vibrations caused by driving the spindle motor with trapezoidal currents can result in undesirable errors during the manufacturing process, such as written-in repeatable run-out (RRO) when servo writing the disk drive with embedded servo sectors, thereby forming eccentric tracks. The extent of written-in RRO limits the data density of the disk drive by limiting the maximum number of tracks per inch (TPI) for the servo system to function properly during normal operation of the disk drive.
U.S. Pat. No. 5,723,957 discloses a sinusoidal spindle motor driver comprising a sine wave amplitude modulating circuit which generates sinusoidal driving waveforms. The sinusoidal driving waveforms drive the windings of the spindle motor while servo track writing the disk drive during production line manufacturing. Although this technique reduces the torque ripple vibrations that cause written-in RRO, it requires integrated Hall effect elements for detecting the angular velocity of the spindle motor which increase the cost and complexity of the spindle motor.
There is, therefore, a need to drive a spindle motor in a disk drive during production line manufacturing in a manner which reduces vibrations without requiring Hall elements to detect the angular velocity of the spindle motor.
The present invention may be regarded as a production line spindle control circuit for manufacturing a disk drive, the disk drive comprising a disk, a head actuated radially over the disk, and a multi-phase spindle motor comprising a plurality of windings for rotating the disk. The production line spindle control circuit comprises a sinusoidal driver for generating a plurality of sinusoidal driving currents. The sinusoidal driving currents are applied to the spindle motor windings over an interface in order to rotate the spindle motor, and a back EMF signal is received over the interface representing a back EMF voltage across at least one of the spindle motor windings. A commutation controller within the production line spindle control circuit applies the sinusoidal driving currents to the spindle motor windings in a commutation sequence in response to the back EMF signal, and controls an angular velocity of the spindle motor in response to the back EMF signal. The interface for attaching to the spindle motor during a manufacturing procedure and for detaching from the spindle motor after the manufacturing procedure.
In one embodiment, the back EMF signal is converted into a square wave having edges defined relative to when the back EMF voltage crosses a predetermined threshold. In one embodiment, the commutation controller changes a state of the commutation sequence relative to the edges of the square wave. In one embodiment, a frequency of the square wave represents the angular velocity of the spindle motor.
In one embodiment, the sinusoidal driver comprises a linear driver for generating substantially linear sinusoidal driving currents. In another embodiment, the sinusoidal driver comprises a pulse width modulating driver for pulse width modulating the sinusoidal driving currents.
In one embodiment, the production line spindle control circuit is used by a servo writer for servo writing embedded servo patterns onto the disk during the manufacturing procedure.
The present invention may also be regarded as a method of manufacturing a disk drive, the disk drive comprising a disk, a head actuated radially over the disk, and a multi-phase spindle motor comprising a plurality of windings for rotating the disk. A production line spindle control circuit is attached to the spindle motor during a manufacturing procedure, wherein the production line spindle control circuit for generating a plurality of sinusoidal driving currents. The production line spindle control circuit receives a back EMF signal from the spindle motor, the back EMF signal representing a back EMF voltage across at least one of the spindle motor windings. The production line spindle control circuit applies the sinusoidal driving currents to the spindle motor windings in a commutation sequence in response to the back EMF signal. The production line spindle control circuit controls an angular velocity of the spindle motor in response to the back EMF signal. The production line spindle control circuit is detached from the spindle motor after the manufacturing procedure.